Análises térmicas e espectroscópicas para a avaliação do perfil físico-químico de amostras comerciais de Paullinia cupana Kunth

Abstract

Paullinia cupana Kunth, better known as Guarana, is a plant that originated in the Amazon, which is very well known in Brazil. The great consumption and the search for this product in the national market are mainly characterized by the ease of access, the low cost of acquisition and being highly appreciated due to its energy properties. Its composition is rich in caffeine, theobromine, and theophylline, which makes guarana an excellent stimulant. Given the economic relevance of guarana to the country and because it is a very consumed product in Brazil, it is extremely important to evaluate the physical and chemical properties of the product that reaches the consumer. The thermoanalytical techniques and the vibrational spectroscopies have been shown potential tools for the characterization of diverse materials and foods. Thus, the objective of this work is to perform thermal and spectroscopic analysis on commercial samples of guarana powder in order to evaluate its physicochemical behavior using thermogravimetric (TG), differential thermal analysis (DTA), derivative thermogravimetry (DTG) and the analysis of the evolved gases by means of the coupling of the thermogravimetry and the spectroscopic in the infrared with Fourier transform (FT-IR). In addition to characterizing the crystal structures by means of X-ray diffraction and a study of the vibrational modes of the compounds by Raman spectroscopy. The results obtained by the TG / DTG analysis show that the mass loss occurs in two stages in all samples, the first corresponding to dehydration and the second due to the thermal decomposition of carbohydrates and other organic compounds. By the DTA technique, three endothermic events were observed, one due to the release of water and the others corresponding to the decomposition of the material. The analyzed samples present similar thermoanalytical profiles in the mass loss intervals and the endothermic events. This similarity suggests that all of them feature characteristically the same composition. The release of water, carbon dioxide and two other unidentified volatile compounds were verified by the TG / FT-IR coupling for the analysis of the released gases. By means of Raman spectroscopy it was possible to verify the vibrational modes of cellulose, lignin, caffeine and theobromine, confirming the presence of plant fibers and methylxanthines in the samples. The X-ray diffraction showed the crystalline structures present in the material corresponding to the crystalline planes of the cellulose. In general, the techniques used were effective to carry out the proposed study of commercial samples of guarana powder.